Unitary filter tank and an underdrain for filtering a body of water

ABSTRACT

Exemplary embodiments include a unitary pool filter tank and/or an underdrain for a pool filter unit. Embodiments of the unitary pool filter tank can have an integrally formed housing and base. The filter tank can be formed using a blow molding process in which the base of the filter tank is includes a support section and a punted section that has an underdrain mounting member. Embodiments of the underdrain can be formed by interlocking top and bottom components. The top and bottom components can be interlocked by inter-component locking structures.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 13/204,377 filed on Aug. 5, 2011, which isincorporated by reference herein in its entirety.

BACKGROUND

1. Field of Technology

Exemplary embodiments include a unitary filter tank and/or an underdrainfor a filtering a body of water.

2. Brief Discussion of Related Art

Swimming pools often use sand filter units to remove particulate andgelatinous contaminants from pool water. A typical sand filter unitincludes a filter tank, a separate base unit upon which the filter tankrests, an underdrain assembly disposed within and towards a bottom ofthe filter tank, and a water circulation system to circulate waterthrough the filter unit. Once the underdrain assembly is in place withinthe filter tank, the filter tank is filled with sand, which covers theunderdrain assembly. In a typical implementation, pool water enters thefilter tank towards a top end via the water circulation system andpercolates through the sand to the underdrain assembly, which collectscleansed pool water for recirculation in the pool by the watercirculation system.

FIG. 63 is an example of a conventional sand filter tank assembly 5000having a filter tank 5010 with a separate base 5050. The filter tank5010 has an opening 5012 at a top end 5014 of the filter tank 5010 andinterface structures 5016 at a bottom end 5018. The opening 5012facilitates communication between an interior and exterior of the filtertank 5010 for the water circulation system. The interface structures5016 can be configured for mounting the filter tank 5010 on the base5050. The base 5050 includes interface structures 5052 for receiving theinterface structures 5016 of the filter tank 5010. In operation, thefilter tank 5010 rests on the base 5050 and is subsequently filled witha filtrate material.

FIGS. 64-68 show an example conventional filter tank manufacturingsystem 6000 and process for forming the filter tank 5010 of FIG. 63. Thesystem 6000 can include an extrusion head 6100, a mold 6200 operativelycoupled to a press 6300, and a blow pin 6400. The mold 6200 can bepartitioned into two sections and can be moveable between an open andclosed position by the press 6300. To form the filter tank, moltenpolymer parison 6110 is extruded between the mold sections by theextrusion head 6100 when the mold 6200 is in the open position. Once asufficient amount of molten polymer parison 6110 has been extruded, thepress 6300 can urge the opposing sections of the mold 6200 together sothat the mold 6200 is in the closed position. In the closed position,the molten polymer parison 6110 is pinched at the ends of the mold 6200to form a molten polymer body 6120. The blow pin 6400 can be introducedinto the mold 6200 and into an interior area of the molten polymer body6120 and can blow or force air into the molten polymer body 6120 toexpand the molten polymer body 6120 outward towards contoured surfacesof the mold 6200 until the molten polymer body conforms to the mold. Theblow pin 6400 can continue to blow, air to cool and harden the moltenpolymer body. Once the molten polymer body 6120 has been sufficientlycooled and hardened, the mold 6200 is opened to release the newly formedfilter tank.

With respect to the underdrain assembly of a filter unit, severalconfiguration have been implemented. In one common implementation, aunderdrain assembly can have several separate parts that can be coupledto form the underdrain assembly during installation of the underdrainassembly in a filter tank. Reference is also made, for example, to U.S.Pat. No. 5,068,033, the contents of which are incorporated herein byreference for all purposes.

SUMMARY

In one aspect, a method of forming a unitary filter tank having anintegral housing and base is disclosed. The unitary filter tank can beconfigured to filter pool water using sand and includes forming a moltenpolymer body with a mold. The method includes forming a molten polymerbody with a mold. The mold has a housing formation area to form thehousing of a unitary filter tank, a base formation area to form the baseof the unitary filter tank, and transition points separating the housingformation area from the base formation area. The method also includesforcing air into the molten polymer body to urge the molten polymer bodyto conform to the mold and urging the molten polymer body inward towardsan interior of the molten polymer body in the base formation area toform a punted section of the base. The punted section forms a generallyconvex inner wall of the unitary filter tank with a bumped out portionformed about a center axis of the filter tank.

In another aspect, a unitary pool filter tank is disclosed. The filtertank includes a housing portion and a base portion. The housing portionreceives a filtrate material and the base portion is integrally formedwith the housing. The base portion includes a punted section and asupport section. The punted section forms a generally convex inner wallportion of the unitary pool filter tank with a bumped out portion formedabout a center axis of the filter tank. The support section integrallyconnects the punted section to the housing portion. The bumped outportion forms an underdrain mounting member corresponding to a filtertank mounting member of an underdrain.

In another aspect, a system for forming a pool filter tank is disclosed.The system includes a mold having an open position to receive a moltenpolymer parison and a closed position to form a molten polymer body fromthe molten polymer parison. The mold includes a housing formation areahaving housing formation molders, a base formation area having baseformation molders, and transition points separating the housingformation area from the base formation area. The housing formationmolders are spaced away from each other in the open position and areproximate to each other in the closed position. The base formationmolders are spaced away from each other and away from the transitionpoints in the open position. The base formation molders are proximate toeach other in the closed position and are moveable towards or away fromthe transition points to form the base portion of the pool filter tank.

In another aspect, a system for filtering pool water is disclosed. Thesystem includes a unitary tank and an underdrain. The unitary filtertank has an integrally formed housing and base. The base includes apunted section and a support structure. The punted section forms agenerally convex inner wall portion of the unitary pool filter tank witha bumped out portion formed about a center axis of the filter tank. Thesupport section integrally connects the punted section to the housingportion. The bumped out portion forms an underdrain mounting member. Thesupport section integrally connects the punted section to the housing.The underdrain has a filter tank mounting member corresponding to theunderdrain mounting member to seat the underdrain on the punted sectionof the base. The underdrain includes interlocking first and secondcomponents, wherein the second component selectively interlocks with thefirst component to form an interior area of the underdrain. The firstand second components have a plurality of drainage openings, each ofwhich open into the interior area of the underdrain and permit fluidcommunication between an exterior and the interior area.

Other objects and features will become apparent from the followingdetailed description considered in conjunction with the accompanyingdrawings. It is to be understood, however, that the drawings aredesigned as an illustration only and not as a definition of the limitsof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary filter unit for filtering water including, forexample, water from a pool, spa, hot tub, aquaculture environment,fountain, pond, or the like.

FIG. 2 is a side view of the filter tank of FIG. 1.

FIG. 3 is a partial cutaway view of the filter tank of FIG. 1.

FIG. 4 is a bottom view of the filter tank along line 4-4 of FIG. 3.

FIG. 5 is a top view of the filter tank along line 5-5 of FIG. 3.

FIG. 6 is a detailed view of area 6 of FIG. 3.

FIGS. 7-12 show an exemplary system and process for forming the filtertank in FIG. 1.

FIG. 13 shows a side view of another exemplary embodiment of a filtertank that can be implemented to facilitate filtering water including,for example, water from a pool, spa, hot tub, aquaculture environment,fountain, pond, or the like.

FIG. 14 is a top view of the filter tank of FIG. 13.

FIG. 15 is a bottom view of the filter tank of FIG. 13.

FIG. 16 is a perspective view of a bottom portion of the filter tank ofFIG. 13.

FIG. 17 is a cross-sectional side view of the filter tank of FIG. 13.

FIG. 18 is a cross-sectional side view of the filter tank of FIG. 13rotated about its center axis by 90° with respect to the cross-sectionalview depicted in FIG. 17.

FIG. 19 is a more detailed view of the base of the filter tank depictedin FIG. 17.

FIGS. 20-25 show an exemplary system and process for forming the filtertank in FIGS. 13-19.

FIG. 26 is a perspective view of an exemplary embodiment of anunderdrain illustrated in FIG. 1.

FIG. 27 is a perspective view of the bottom component of the underdrainof FIG. 26.

FIG. 28 is a side view of the bottom component of the underdrain of FIG.27.

FIG. 29 is a bottom view of the bottom component of the underdrain ofFIG. 27.

FIG. 30 is a cross-sectional view of the bottom component of theunderdrain along the line 30-30 of FIG. 28.

FIG. 31 is a top view of the bottom component along line 31-31 of FIG.29.

FIG. 32 is a cross-sectional view of the bottom component of theunderdrain along the line 32-32 of FIG. 30.

FIG. 33 is a cross-sectional view of the bottom component of theunderdrain along the line 33-33 of FIG. 31.

FIG. 34 is a detailed view of area 34 in FIG. 33.

FIG. 35 is a detailed view of area 35 in FIG. 33.

FIG. 36 is a perspective view of the top component of the underdrain ofFIG. 27.

FIG. 37 is a side view of the top component of the underdrain of FIG.36.

FIG. 38 is a bottom view of the top component of the underdrain of FIG.36.

FIG. 39 is a cross-sectional view of the top component of the underdrainalong the line 39-39 of FIG. 38.

FIG. 40 is a detailed view of area 40 in FIG. 39.

FIG. 41 is a cross-sectional view of the top component of the underdrainalong the line 41-41 of FIG. 37.

FIG. 42 is a cross-sectional view of the top component of the underdrainalong the line 42-42 of FIG. 37.

FIG. 43 is a detailed view of area 43 in FIG. 41.

FIG. 44 is a cross-sectional view of the top component of the underdrainalong a line 43-43 of FIG. 38.

FIG. 45 is a perspective view of another exemplary embodiment of anunderdrain.

FIG. 46 is a cross-sectional view of the assembled underdrain of FIG. 45along line 46-46.

FIG. 47 is a side view of the bottom component of the underdrain of FIG.45.

FIG. 48 is a top view of the bottom component of FIG. 45.

FIG. 49 is a cross-sectional view along the line 49-49 of FIG. 48.

FIG. 50 is cross-sectional view along line 50-50 of FIG. 47.

FIG. 51 is a cross-sectional view along line 51-51 of FIG. 50.

FIG. 52 is a detailed view of area 52 of FIG. 48.

FIG. 53 is a side view of the top component of the underdrain of FIG.45.

FIG. 54 is a bottom view of the top component of FIG. 45.

FIG. 55 is a cross-sectional view along the line 55-55 of FIG. 54.

FIG. 56 is a cross-sectional view along the line 56-56 of FIG. 54.

FIG. 57 is a cross-sectional view along line 57-57 of FIG. 53.

FIG. 58 is a cross-sectional view along line 58-58 of FIG. 53.

FIG. 59 is a cross-sectional view along line 59-59 of FIG. 58.

FIG. 60 is a detailed view of area 60 of FIG. 54

FIG. 61 is a graph of pressure loss for a conventional lateralunderdrain assembly and for an exemplary underdrain of the presentdisclosure.

FIG. 62 is a graph of experimental results for a dirt loading test.

FIG. 63 is a prior art filter tank assembly having a housing with aseparately attachable base section.

FIGS. 64-68 show a prior art system and process for forming a filtertank of FIG. 63.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present disclosure include a unitary filtertank and/or an underdrain for filtering water from a body of water, suchas a swimming pool, hot tub, spa, aquaculture environment, pond,fountain, and the like. Embodiments of the unitary filter tank can havean integrally formed housing and base. The unitary filter tank can beformed using a blow molding process in which the base of the unitaryfilter tank is reinforced using multiple layers of a polymer that havebeen folded and/or pinched together. The base of the unitary filter tankcan provide a durable platform to support the filter tank when thefilter tank is loaded with a filtrate material, such as sand, and water.Embodiments of the underdrain can be formed by interlocking top andbottom components that can be interlocked by inter-component lockingstructures. Exemplary embodiments of the underdrain provide anefficiently manufactured and easy-to-install underdrain, which canreduce the cost and burden associated with conventional underdrainswhile maintaining performance that is comparable to some conventionalunderdrain assemblies.

FIG. 1 shows an exemplary filter unit 100. The filter unit 100 can beconfigured to receive water to be filtered from a pool or other body ofwater and can process the water to remove contaminants and gelatinousmaterial. After the filter unit 100 filters the water, the filteredwater is returned to the pool or other body of water. The filter unit100 can include a unitary filter tank 1000, an underdrain 2000, and acover assembly 3000.

The filter tank 1000 can include of an integrally formed housing 1100and a base 1500, and can define an interior area 1010 within which theunderdrain 2000 and a filtrate material 1020, such as sand, can bedisposed. The housing 1100 can include a first port 1110 positionedopposite of the base 1500 to facilitate communication between aninterior and an exterior of the filter tank 1000. In some embodiments,the filter tank 1000 can include other ports to facilitate communicationbetween an interior and exterior of the filter tank 1000, such as asecond port 1120 disposed proximate to the base 1500 to facilitatedraining of the filter tank 1000. The base 1500 can be formed to supportand provide a platform for the filter tank 1000. In some embodiments,the filter tank 1000 can be formed from a polymer, such as athermoplastic. For example, in some embodiments, the filter tank 1000can be formed from high density polyethylene. The filter tank 1000 canbe formed using a blow molding process in which the filter tank 1000 isformed using a gas, such as air, to shape a molten polymer bodyaccording to a mold. Exemplary embodiments of the filter tank 1000 aredescribed in more detail below with reference to FIGS. 1-12.

The underdrain 2000 can be formed of detachably coupled components andcan have drainage openings 2200 and 2700. For example, the underdrain2000 can include two components that are selectively interlocked usinginter-component locking structures, which can form a snap fit betweenthe components. The drainage openings 2200 and 2700 can be configured topermit water to pass through to an interior of the underdrain 2000 froman exterior of the underdrain 2000, but to prevent the filtrate material1020, such as sand, from entering the interior of the underdrain 2000.In some embodiments, the underdrain 2000 can be formed using a polymer,such as polystyrene, polypropylene, or another plastic or plastic-likematerial, and can have a generally rectangular configuration withrounded sides and/or corners and a generally hollow interior area.Exemplary embodiments of the underdrain 2000 are described in moredetail below with references to FIGS. 1 and 26-43.

The cover assembly 3000 can include a cover 3100, a diffuser 3200, aninlet port 3110, and an outlet port 3120. The inlet port 3110 canreceive water to be filtered by the filter unit 100 from a watercirculation system (not shown) and the outlet port 3120 can output waterthat has been filtered by the filter unit 100 to the water circulationsystem (not shown) for recirculation. The inlet port 3110 can beoperatively coupled to a conduit 3130, such as a hose, through whichwater to be filtered flows to the filter unit 100 from the pool or otherbody of water. The outlet port 3120 can be operatively coupled to arecirculation pipe 3300 to facilitate fluid communication between theunderdrain 2000 and the outlet port 3120, and can be operatively coupledto conduit 3140, such as a hose, through which water that has beenfiltered flows from the filter unit 100 for recirculation in the pool orother body of water. The inlet port 3110 can be in communication withthe diffuser 3200 such that water flowing into the cover 3100 from thepool passes through the diffuser 3200. The diffuser 3200 distributes thewater at or near the top of the filter tank 1000. In some embodiments,the diffuser 3200 can be configured to distribute the water into thetank uniformly. Once the water percolates through the filtrate material1020 and is collected by the underdrain 2000, the filtered water isdrawn up through the recirculation pipe 3300 by the pump 3400, which canbe in communication with the outlet port 3120.

In some embodiments, the cover assembly 3000 can implement a multi-portvalve controlled by an actuator (not shown) that facilitates flowreversal of the water through the filter unit 100 to switch between anormal and backwash operation. The multi-port valve can be actuated tooperatively couple the conduit 3130 to the recirculation pipe 3300 suchthat the conduit 3130 is in fluid communication with the recirculationpipe 3300 to implement a backwash operation.

A pump 3400, shown as being downstream of the filter unit 1000 in FIG.1, can be configured to draw the filtered water from the filter unit 100through the recirculation pipe 3300 and the outlet port 3120.Alternatively, or in addition, a pump (not shown) can be positionedupstream of the filter unit 100 to generate a flow of water from thepool or other body of water into the filter unit 100.

Referring to FIGS. 1-6, the housing 1100 of the filter tank 1000 canhave a wall 1130 with a generally spherical configuration and agenerally uniform wall thickness 1140 (FIG. 2). While the wall 1130 ofthe present embodiment is generally spherical, those skilled in the artwill recognize that other configurations can be implemented. Forexample, in some embodiments the wall 1130 can have a generallycylindrical configuration, rectangular configuration, pear-shapedconfiguration, and the like. Furthermore, while the wall thickness 1140is generally uniform, those skilled in the art will recognize that thewall thickness 1140 may vary. For example, the wall thickness 1140 canincrease near the base 1500 and/or the uniformity of the wall thickness1140 may vary due to manufacturing tolerances.

The first port 1110 can be disposed in the wall 1130 opposite the base1500 of the filter tank 1000. The first port 1110 can allow access to aninterior area 1010 of the filter tank 1000 and can provide a passagewaybetween the interior and exterior of the filter tank 1000. A neck orcollar section 1160 can provide a transition from the generallyspherical shape of the housing 1100 to a generally cylindrical shapeassociated with the first port 1110. The collar section 1160 associatedwith the first port 1110 can include an interface 1170, such as a lip,gasket, threaded surface, flange, and the like, for receiving a cover toclose and/or seal the first port 1110. In one implementation, the cover3100 can be used to form a water tight seal with the first port 1110.

In some embodiments, a second port 1120 can be formed in the housing1100 proximate to the base 1500. The second port 1120 can be configuredto drain the interior area 1010 of the filter tank 1000. A spout 1180can be disposed with respect to the second port 1120 and can be threadedto threadingly engage a hose and/or other object, such as a cap. Thespout 1180 can be closed by a valve or a cap 1190 to form a water tightseal so that when contents are disposed within the housing 1100, thecontents do not escape through the second port 1120.

While the ports 1110 and 1120, have been illustrated at particularlylocations on the housing 1100, and the inlet ports 3110 and 3120 havebeen illustrated as part of the cover assembly 3000, those skilled inthe art will recognize one or more of the ports 1110, 1120, 3110, and3120 can be disposed in other locations with respect to the housing. Forexample, one or more of the ports can be disposed, independently orotherwise, at one or more different locations, such as on a side of thehousing.

Referring to FIGS. 1, 3, and 6, for example, the base 1500 can have apunted section 1510 protruding into the interior area 1010 of the filtertank 1000 and a filter tank support structure 1610 that can have agenerally cylindrical ring configuration. The punted section 1510 of thebase 1500 can form a bottom wall portion 1520 of the filter tank 1000.The bottom wall portion 1520 can protrude and/or extend into the housing1100 and can form a convex interior wall in the interior area 1010 ofthe filter tank 1000 (or a concave exterior wall of the filter tank1000) such that a cross-section of the punted section 1510 has agenerally curved, dome, and/or parabolic shape. In some embodiments, awall thickness 1530 of the punted section 1510 can be substantiallyequal to the wall thickness 1140 of the housing 1100. In someembodiments, the wall thickness 1530 of the punted section 1510 can begreater than the wall thickness 1140 of the housing 1100.

Underdrain mounting members 1540 can be disposed on an interior surfaceof the bottom wall portion 1520 to provide an area for mounting anunderdrain within the filter tank 1000. The underdrain mounting members1540 can have a complementary structure to filter tank mounting membersof an underdrain so that the underdrain mounting members 1540 and thefilter tank mounting members can be aligned to seat the underdrain onthe bottom wall portion 1520. In some embodiments, the underdrainmounting members 1540 can be formed as grooves or channels on the bottomwall portion 1520. For example, the underdrain mounting members 1540 canbe curved grooves configured to receive and/or capture the correspondingfilter tank mounting members of the underdrain. In the presentembodiment, a pair of underdrain mounting members 1540 can be positionedin an opposing relation so that opposing ends of the underdrain mountingmembers 1540 are aligned and the concave portions of the curvedunderdrain mounting members 1540 face each other.

The support structure 1610 of the base can integrally connect the puntedsection 1510 of the base 1500 to the housing 1100 and can provide a andreinforced stand for supporting the weight of the filter tank 1000 whenthe filter tank 1000 is loaded with a filtrate material (e.g., sand) andwater. The support structure 1610 can include foot sections 1620 toprovide points of contact between the filter tank 1000 and a surfaceupon which the filter tank 1000 is supported. An outer surface 1630 ofthe support structure 1610 can be contoured to flare outward atproximate and distal ends 1640 and 1650 of support structure 1610 suchthat an outer diameter of the base 1500 is greater at proximate anddistal ends 1640 and 1650, respectively, than an outer diameter of thesupport structure 1610 between the proximate and distal ends 1640 and1650.

The support structure 1610 can be formed by pinching, pressing, and/orfolding layers of a molten polymer together during a manufacturingprocess of the filter tank 1000. For example, a mold used to form thefilter tank 1000 can be configured to fold and/or pinch layers of moltenpolymer together about an outward bend 1690 to form a support structurewith reinforced walls to securely support the load applied by the filtertank when the filter tank 1000 is filled with the filtrate material(e.g., sand) and water. As one example, at least two layers of moltenpolymer can be used to form the support structure 1610. In someembodiments, the support structure 1610 can have a thickness 1660 thatis at least about 25 to about 300 percent thicker than the wall 1130 ofthe housing 1100 or about 75 percent to about 150 percent thicker thanthe wall 1130 of the housing 1100.

In some embodiments, the support structure 1610 can have a thickness1660 that is about twice the wall thickness 1140 of the wall 1130, suchthat the support structure 1610 forms a “double wall”. For example, asshown in FIGS. 1, 3, and 6, the support structure 1610 can be formed bya first polymer layer 1670 extending between the outward bend 1690 andan inward bend 1695 and a second polymer layer 1680 on the other side ofthe outward bend 1690. The first and second polymer layers 1670 and 1680can be pinched or folded together during the filter tank manufacturingprocess. While FIGS. 1, 3, and 6 are illustrative of a double wall,those skilled in the art will recognize, that additional layers ofpolymer can be folded and/or pinched together to form a thicker supportstructure.

In some embodiments, the thickness 1660 of the support structure 1610can be specified to support a total weight of the filter tank after thefiltrate material and water have been added. By using folded layers ofpolymer, the support structure 1610 is strengthened and reinforced tobare the load applied by the filter tank 1000 in operation and providesa base for the filter tank 1000. Forming the filter tank as a unitarystructure having an integrally formed housing and reinforced baseprovides a cost effective, and durable filter tank for filtration ofpool water.

In exemplary embodiments, the filter unit 100 can be a “sand filter”unit for filtering water from a pool, spa, hot tub, aqua-cultureenvironment, fountain, or the like, using sand as a filtrate material.In such embodiments, the sand disposed within the housing 1100 of thefilter tank 1000 can result in a large load to be supported by theintegral base 1500 of the filter tank 1000. For example, a typical loadfrom the sand can be in the range of about forty (40) to about threehundred fifty (350) pounds. In conventional sand filter designs, thebase and filter tank are typically separately constructed. By allowingthe base to be fabricated separately from the housing, the differentprocesses, materials, structures, and the like can be used to constructa base with sufficient strength to support the load of the sand.However, requiring separate fabrication of the housing and the baseresults in a manufacturing process that can be less than optimal. Inexemplary embodiments the housing and base are concurrently andintegrally formed using the same material and the same fabricationprocess so that the base and the housing form an integral unitary filtertank 1000. To support the load of the sand exemplary embodiments formthe section using layers of polymer in the base that are folded,pressed, and/or pinched together during the manufacturing process of theunitary filter tank 100.

FIGS. 7-12 show an exemplary filter tank manufacturing system 4000 andprocess for forming a unitary filter tank having an integrally formedhousing and base. For example, embodiments of the manufacturing system4000 and process can be implemented to form embodiments of the filtertank 1000 (FIGS. 1-6). The system 4000 can include an extrusion head4100, a mold 4200 operatively coupled to presses 4500 and 4600, and ablow pin 4700. The extrusion head 4100 can extrude molten polymerparison 4110 to be shaped using the mold 4200 and the blow pin 4700. Insome embodiments, the molten polymer parison 4110 can be extruded fromthe extrusion head 4100 in a generally cylindrical shape.

The mold 4200 can be partitioned into housing formation area 4210including housing formation molders 4220 and 4230 and base formationarea 4240 including base formation molders 4250 and 4260. The housingformation area 4210 facilitates formation of the housing portion of thefilter tank and the base formation area 4240 facilitate formation of thebase portion of the filter tank. The housing formation molders 4220 and4230 can include contoured surfaces 4222 and 4232, respectively,corresponding to an exterior surface of the housing to be formed usingthe mold 4200. For example, in some embodiments, the contoured surfaces4222 and 4232 can be generally semispherical such that when the mold4200 is closed, the molders 4220 and 4230 are brought together and thecontoured surfaces 4222 and 4232 form a generally spherical cavity. Inexemplary embodiments, the molders 4220 and 4230 can be configured toform the port 1110 of the housing 1000. For example, the molders 4220and 4230 can include contoured or notched surfaces 4226 and 4236 forforming the collar 1160 and interface portions 1170 of the housing 1000(e.g., FIGS. 1-3 and 5).

In the present embodiment, transition points 4270 and 4280 separate thehousing formation area 4210 from the base formation area 4240. Thetransition points 4270 and 4280 can form triangular tooth-like segmentsprotruding inwardly into the mold cavity 4300. The transition points4270 and 4280 can operate to form a transition area between the housingand base of the filter tank to be formed using the mold 4200.Furthermore, the transition points 4270 and 4280 can operate to form theinward bend 1695 in the molten polymer during filter tank formation tofacilitate folding, pressing, and/or pinching of the molten polymer inthe base formation area to form the support structure 1610 of the base1500.

The housing formation molders 4220 and 4230 and the base formationmolders 4250 and 4260 can be moveable along the x-axis 4202 by the press4500 to close the mold 4200 and form a mold cavity 4300. For example,the press 4500 can be configured to urge opposing molders towards eachother as indicated by arrows 4510 (FIG. 8) to close the mold. When themold 4200 is closed (e.g., FIGS. 9-11), the housing formation molders4220 and 4230 of the mold 4200 abut at a distal end 4320 of the mold4200 and the base formation molders 4250 and 4260 of the mold 4200 abutat a proximate end 4330 of the mold 4200. Closing the mold 4200 on amolten polymer parison 4110 extrusion extending between and beyond theproximate and distal ends 4330 and 4320 of the mold 4200 pinches themolten polymer parison 4110 together at the proximate and distal ends4330 and 4320 of the mold 4200 to form a molten polymer body 4340 to beshaped to conform to the contoured surfaces of the molders.

The base formation molders 4250 and 4260 can include contoured surfaces4252 and 4262 corresponding to the punted section 1510 and the supportstructure 1610 of the base 1500 (FIG. 1). For example, each of themolders 4250 and 4260 can include a generally curved, arc-like surfacesuch that when the molders 4250 and 4260 are pressed together along thex-axis 4202 by the press 4500, the molders 4250 and 4260 form a convexsurface extending into the mold cavity 4300, where a cross-section ofthe convex surface is curved and/or parabolic, as shown in FIGS. 8-10.The contoured surfaces 4252 and 4262 can also include contoured orprotruding portions 4254 and 4264, respectively, for forming theunderdrain mounting members 1540. While contoured portions 4254 and 4264have been illustrated as protruding from the contoured surfaces 4252 and4262, respectively, those skilled in the art will recognize that thecontoured surfaces 4254 and 4264 can be recessed in the contouredsurfaces 4252 and 4262, respectively. Thus, in exemplary embodiments,the underdrain mounting members 1540 can be raised, recessed, orotherwise formed in or on the punted section. The base formation molders4250 and 4260 can be moveable along the x-axis 4202 by the press 4500 toclose the mold 4200 and form the mold cavity 4300. Additionally, thebase formation molders 4250 and 4260 can be moveable by the press 4600along a y-axis 4204 to urge the molders 4250 and 4260 towards or awayfrom the transition points 4270 and 4280, respectively.

Referring to FIGS. 10 and 11, for example, the blow pin 4700 can forceair into a molten polymer body 4340 formed upon closing the mold 4200 onextruded molten polymer parison 4110. The forced air can urge the moltenpolymer body 4340 to conform to the contoured surfaces of the mold 4200.The blow pin 4700 can also introduce air to cool and harden the moltenpolymer body 4340. The blow pin 4700 is generally moveable along they-axis 4204 to move a distal end 4710 of the blow pin 4700 into and outof the mold area 4290 and/or the mold cavity 4300.

Referring to FIGS. 7-12, an exemplary embodiment of the filter tankmanufacturing process can begin with the mold 4200 in an open position.In the open position, as shown in FIGS. 7 and 8, the molders 4220 and4230 are separated and the molders 4250 and 4260 are separated.Additionally, the molders 4250 and 4260 are raised away from thetransition points 4270 and 4280, respectively. A polymer resin, such asa high density polyethylene, can be heated to form the molten polymerparison 4110 extruded by the extrusion head 4100. The extrusion head4100 extrudes the molten polymer parison 4110 into the mold area 4290 sothat the molten polymer parison 4110 extends between and beyondproximate and distal ends 4330 and 4320 of the mold 4200. Once asufficient amount of molten polymer parison 4110 has been extruded, thepress 4500 can urge opposing molders of the mold 4200 along the x-axis4202, as shown by arrows 4510 (FIG. 8), so that the mold 4200 closes andthe molten polymer parison 4110 is pinched at the proximate and distalends 4330 and 4320 of the mold 4200 to create the molten polymer body4340 within the mold cavity 4300, as shown in FIG. 9.

Before, during, or after closing the mold 4200, the blow pin 4700 can beintroduced into the mold cavity 4300, as indicated by arrow 4710 in FIG.9. The blow pin 4700 can extend into an interior area of the moltenpolymer body 4340. In the mold closed position, as shown in FIGS. 10 and11, for example, the blow pin 4700 can blow or force air into the moltenpolymer body 4340 expanding the molten polymer body 4340 to urge orforce the molten polymer outward towards the contoured surfaces of themold 4200. As the molten polymer body 4340 expands, the molten polymerbody 4340 presses against the contoured surfaces 4222 and 4232 to formthe housing, and presses against the contoured surfaces 4226 and 4236 toform the first port 1110. As the molten polymer body 4340 expands, themolten polymer body 4340 also presses against the transition points 4270and 4280 so that the transition points 4270 and 4280 have a bottlenecklike effect on the body 4340 to bend the molten polymer body 4340 inwardabout the transition points 4270 and 4280 to create the inward bend 1695in a portion of the molten polymer body 4340. As the molten polymer body4340 continues to expand, the molten polymer body 4340 is urged againstthe base formation molders 4250 and 4260 to form the outward bend 1690in the molten polymer body 4340 between the base formation molders 4250and 4260 and the transition points 4270 and 4280. The first layer 1670is defined between the inward bend 1695 and the outward bend 1690 andthe second layer 1680 is formed by the outward bend 1690.

Referring to FIGS. 10 and 11, once the body 4340 is expanded so that theinward bend 1695 and outward bend 1690 are formed in the molten polymerbody 4340, the base formation molders 4250 and 4260 can be lowered bythe press 4600 along the y-axis 4204, as indicated by arrows 4610,towards the transition points 4270 and 4280 to press the second polymerlayer 1680 against the first polymer layer 1670. As the base formationmolders 4250 and 4260 push the molten polymer in the base formation area4240 towards the transition points 4270 and 4280, respectively, the baseformations molders 4250 and 4260 can fold, press, and/or pinch the firstand second layers 1670 and 1680 between the base formation molders 4250and 4260 and the transition points 4270 and 4280, respectively, and canform the convex inner surface of the punted section 1510 as well as theunderdrain mounting members 1540. Once the base formation molders 4250and 4260 have been fully lowered the second polymer layer 1680 is foldedupon the first polymer layer 1670 and/or pinched between the baseformation molders 4250 and 4260 and the transition points 4270 and 4280to form the support structure 1610 of the base 1500 and the curvedsurfaces of the base formation molders between the transition pointsform the convex punted section 1510.

The blow pin 4700 can continue to blow air to cool and harden the moltenpolymer. Once the molten plastic has been sufficiently cooled andhardened, the press raises the base formation molders 4250 and 4260along the y-axis 4204 away from the transition points 4270 and 4280, asindicated by arrows 4620, opens the mold 4200 by moving the opposingmolders of the mold 4200 away from each other, as indicated by arrows4520, and lowers the blow pin 4700, as indicated by 4720, to release thenewly formed filter tank.

FIGS. 13-19 show another exemplary filter tank 1000′ that can beimplemented in accordance with one or more embodiments of the filterunit 100. As shown in FIG. 13, embodiments of the filter tank 1000′ caninclude a housing 1100′, which can be integrally formed with a base1500′. The housing 1100′ can have identical or substantially identicalcomponents and features as the housing 1100 described above, except thatthe housing 1100′ can have a generally oval or elliptical shape. Forexample, housing 1100′ can include the port 1110 having the collarsection 1160 and interface 1170, and can include the port 1120. Thefilter tank 1000′ can define an interior area 1010′ within which anunderdrain, such as embodiments of the underdrain 2000, and a filtratematerial 1020, such as sand, can be disposed. In some embodiments, thefilter tank 1000′ can be formed from a polymer, such as a thermoplastic.For example, in some embodiments, the filter tank 1000′ can be formedfrom high density polyethylene. While the shape of the housing 1100′ inthe present embodiment is oval or elliptical, one skilled in the artwill recognize that the housing can have a generally cylindrical,rectangular, spherical, pear-shaped configuration, or any other suitableconfiguration.

The base 1500′ can be formed to support and provide a stable platformfor the filter tank 1000′ and can be formed to securely support the loadapplied by the filter tank 1000′ when the filter tank 1000′ is filledwith the filtrate material (e.g., sand) and water. Referring to FIGS.16-19, for example, the base 1500′ can have a punted section 1510′protruding into the interior area 1010′ of the filter tank 1000′ and afilter tank support section 1610′ that can have a generally ringconfiguration. The punted section 1510′ of the base 1500′ can form abottom wall portion 1520′ of the filter tank 1000′ and can protrudeand/or extend into the interior of the housing 1100′. The bottom wallportion 1520′ can form a generally convex interior wall in the interiorarea 1010′ of the filter tank 1000′ (or a concave exterior wall of thefilter tank 1000′) such that a cross-section of the punted section 1510′has a generally curved, dome, and/or parabolic shape modified by a bumpout 1512′, which forms an underdrain mounting member 1540′ that extendsinto the housing 1100′. In some embodiments, a wall thickness 1530′ ofthe punted section 1510′ can be substantially equal to the wallthickness 1140 of the housing 1100. In some embodiments, the wallthickness 1530′ of the punted section 1510′ can be greater than the wallthickness 1140 of the housing 1100′.

The underdrain mounting member 1540′ can be formed by the bump out 1512′can be a generally cylindrical shape having a rounded upper surface1514′ being formed on an interior surface of the bottom wall portion1520′ to provide an area for mounting an underdrain within the filtertank 1000. The underdrain mounting member 1540′ can have a complementarystructure to filter tank mounting members of an underdrain so that theunderdrain mounting members 1540′ and the filter tank mounting memberscan be aligned to seat the underdrain on the bottom wall portion 1520.In some embodiments, the underdrain mounting member 1540′ of the filtertank 1000′ and the filter tank mounting member(s) of the underdrain canfor a friction fit interconnection so that the underdrain can beremovably secured to the bottom of the filter tank 1000′.

The support section 1610′ of the base 1500′ can integrally connect thepunted section 1510′ of the base 1500′ to the housing 1100′ and canprovide a stable structure for supporting the weight of the filter tank1000′ when the filter tank 1000′ is loaded with a filtrate material(e.g., sand) and water. The support section 1610′ can be formed from anouter surface 1630′, and under surface 1615, and the external surface1522′ of the punted section 1510′. In the present embodiment, the outersurface 1630′ extends generally downward from the bend 1692′ in thehousing 1100′ to a bend 1694′, which defines a boundary between theouter surface 1630′ and the under surface 1615. An outer surface 1630′of the support section 1610′ can be contoured to flare slightly outwardat proximate and distal ends 1640′ and 1650′ of support section 1610such that an outer diameter of the base 1500′ is greater at proximateand distal ends 1640′ and 1650′, respectively, than an outer diameter ofthe support section 1610′ between the proximate and distal ends 1640′and 1650′.

The under surface 1615 can extend radially inward from the bend 1694′ toa bend 1696′, which defines a boundary between the under surface 1615and the external surface 1522′ of the punted section 1510′. The undersurface can include upwardly bending grooves 1618′ that form footsections 1620′ in the under surface 1615. The foot sections 1620′ canprovide contact locations between the filter tank and a support section,such as, for example, the ground, a floor, a platform, or any othersuitable support section.

In some embodiments, the bend 1694′ can form an approximate 90° anglesuch that the under surface 1615 at least initially extends generallyperpendicularly to the outer surface 1630′. The bend 1696′ can define aninitial curvature of the punted section 1510′ and can be greater thanapproximately 90° so that the punted section 1510′ extends upwardly intothe interior area of the filter tank 1000′ and inwardly towards thecenter axis 1002′ of the filter tank 1000′. In some embodiments, thebends 1694′, 1696′ can form different angles, such that, for example,the bends 1694′, 1696′ form angles that are less than or greater than90° and/or such that the angle of bend 1694′ is different from the angleformed by bend 1696′.

As shown in FIGS. 16-19, the base 1500′ can also include at least onebrace 1516′ to reinforce the punted section 1510′ of the base 1500′ aswell as to reinforce the base 1500′ itself. For example, the brace 1516′can be configured to aid in carrying and distributing the load of thefiltrate material (e.g., sand) and water in the filter tank from thepunted section to the support section upon which the filter tank 1000′rests. In the present embodiment, the brace 1516′ can be a cross bracehaving length that extends across an inner diameter of the base 1500′and a width 1518′. A bottom edge 1515′ of the brace 1516′ can extendgenerally linearly along the length of the brace 1516′ and an upper edge1517′ of the brace can conform to the contour of the punted section1520′ such that the upper edge 1517′ has a generally convex shape with abumped out portion 1519′ corresponding to the bump out 1512′ in thepunted section 1510′. In exemplary embodiments, the brace 1516′ can beintegrally formed with the base 1500′.

FIGS. 20-25 show another exemplary filter tank manufacturing system4000′ and process for forming a unitary filter tank having an integrallyformed housing and base. For example, embodiments of the manufacturingsystem 4000′ and process can be implemented to form embodiments of thefilter tank 1000′ (FIGS. 13-19). The system 4000′ can include theextrusion head 4100, the presses 4500 and 4600, and the blow pin 4700 asdescribed above with respect to the system 4000. A mold 4200′ can beoperatively coupled to the presses 4500 and 4600.

The mold 4200′ can be partitioned into a housing formation area 4210′including housing formation molders 4220′ and 4230′ and a base formationarea 4240′ including base formation molders 4250′ and 4260′. The housingformation molders 4220′ and 4230′ can include contoured surfaces 4222′and 4232′, respectively, corresponding to an exterior surface of thehousing to be formed using the mold 4200′. For example, in someembodiments, the contoured surfaces 4222′ and 4232′ can be generallysemioval or semielliptical such that when the mold 4200′ is closed, themolders 4220′ and 4230′ are brought together and the contoured surfaces4222′ and 4232′ form a generally oval or elliptical cavity. In exemplaryembodiments, the molders 4220′ and 4230′ can be configured to form theport 1110 (FIG. 13) of the housing 1000′. For example, the molders 4220′and 4230′ can include the contoured or notched surfaces 4226 and 4236for forming the collar 1160 and interface portions 1170 of the housing1000′ (e.g., FIG. 13).

In the present embodiment, transition points 4270′ and 4280′ separatethe housing formation area 4210′ from the base formation area 4240′. Thetransition points 4270′ and 4280′ can form slight blunt inwardprotrusions into the mold cavity 4300′. The transition points 4270′ and4280′ can operate to form a transition area between the housing and baseof the filter tank to be formed using the mold 4200′. Furthermore, thetransition points 4270′ and 4280′ can operate to form the bend 1692′ inthe molten polymer during filter tank formation to facilitate formationof the base 1500′.

The housing formation molders 4220′ and 4230′ and the base formationmolders 4250′ and 4260′ can be moveable along the x-axis 4202 by thepress 4500 to close the mold 4200′ and form a mold cavity 4300′. Forexample, the press 4500 can be configured to urge opposing molderstowards each other as indicated by arrows 4510 (FIG. 21) to close themold. When the mold 4200′ is closed (e.g., FIGS. 22-24), the housingformation molders 4220′ and 4230′ of the mold 4200′ abut at a distal end4320′ of the mold 4200′ and the base formation molders 4250′ and 4260′of the mold 4200′ abut at a proximate end 4330′ of the mold 4200′. Inexemplary embodiments, when the mold 4200′ is closed, the molders 4250′and 4260′ can form a cavity 4265′ for forming a brace of the base, suchas brace 1516′. Closing the mold 4200′ on a molten polymer parison 4110′extrusion extending between and beyond the proximate and distal ends4330′ and 4320′ of the mold 4200′ and pinches the molten polymer parison4110′ together at the proximate and distal ends 4330′ and 4320′ of themold 4200 to form a molten polymer body 4340′ to be shaped to conform tothe contoured surfaces of the molders.

The base formation molders 4250′ and 4260′ can include contouredsurfaces 4252′ and 4262′ corresponding to the punted section 1510′ andthe support section 1610′ of the base 1500′ (FIGS. 13-19). For example,each of the molders 4250′ and 4260′ can include a generally curved,arc-like surface extending over at least a portion of the molders 4250′and 4260′ such that when the molders 4250′ and 4260′ are pressedtogether along the x-axis 4202 by the press 4500, the molders 4250′ and4260′ form a convex surface extending into the mold cavity 4300′, wherea cross-section of the convex surface is generally curved and/orparabolic. The contoured surfaces 4252′ and 4262′ can also includecontoured or protruding portions 4254′ and 4264′, respectively, forforming the bump out 1512′ corresponding to the underdrain mountingmember 1540′. While contoured portions 4254′ and 4264′ have beenillustrated as protruding from the contoured surfaces 4252′ and 4262′,respectively, those skilled in the art will recognize that the contouredsurfaces 4254′ and 4264′ can be recessed in the contoured surfaces 4252′and 4262′, respectively. Thus, in exemplary embodiments, the underdrainmounting members 1540′ can be raised, recessed, or otherwise formed inor on the punted section. The base formation molders 4250′ and 4260′ canbe moveable along the x-axis 4202 by the press 4500 to close the mold4200′ and form the mold cavity 4300′. Additionally, the base formationmolders 4250′ and 4260′ can be moveable by the press 4600′ along they-axis 4204 to urge the molders 4250′ and 4260′ towards or away from thetransition points 4270′ and 4280′, respectively.

Referring to FIGS. 20-25, an exemplary embodiment of a filter tankmanufacturing process can begin with the mold 4200′ in an open position.In the open position, as shown in FIGS. 20 and 21, the molders 4220′ and4230′ are separated and the molders 4250′ and 4260′ are separated.Additionally, the molders 4250′ and 4260′ are raised away from thetransition points 4270′ and 4280′, respectively. The extrusion head4100′ extrudes the molten polymer parison 4110′ into the mold area 4290′so that the molten polymer parison 4110′ extends between and beyondproximate and distal ends 4330′ and 4320′ of the mold 4200′. The press4500′ can urge opposing molders of the mold 4200′ along the x-axis 4202,as shown by arrows 4510 (FIG. 21), so that the mold 4200′ closes and themolten polymer parison 4110′ is pinched at the proximate and distal ends4330′ and 4320′ of the mold 4200′ to create the molten polymer body4340′ and form the brace 1516′ within the mold cavity 4300′, as shown inFIG. 22.

The blow pin 4700 can extend into an interior area of the molten polymerbody 4340′ and can blow or force air into the molten polymer body 4340′expanding the molten polymer body 4340′ to urge or force the moltenpolymer outward towards the contoured surfaces of the mold 4200′ (FIGS.23-24). As the molten polymer body 4340′ expands, the molten polymerbody 4340′ presses against the contoured surfaces 4222′ and 4232′ toform the housing, and presses against the contoured surfaces 4226′ and4236′ to form the first port 1110. As the molten polymer body 4340′expands, the molten polymer body 4340′ also presses against thetransition points 4270′ and 4280′ so that the transition points 4270′and 4280′ have a bottleneck like effect on the body 4340′ to bend themolten polymer body 4340′ inward about the transition points 4270′ and4280′ to create the inward bend 1692′ in a portion of the molten polymerbody 4340′. As the molten polymer body 4340′ continues to expand, themolten polymer body 4340 ‘is urged against the base formation molders4250’ and 4260′ to form the outward bends 1694′, 1696′ in the moltenpolymer body 4340′ between the base formation molders 4250′ and 4260′and the transition points 4270′ and 4280′.

Referring to FIGS. 23 and 24, once the body 4340′ is expanded so thatthe inward bend 1692′ and outward bends 1694′, 1696′ are formed in themolten polymer body 4340′, the base formation molders 4250′ and 4260′can be lowered by the press 4600 along the y-axis 4204, as indicated byarrows 4610, towards the transition points 4270′ and 4280′ to form theconvex inner surface of the punted section 1510′ as well as theunderdrain mounting members 1540′. Once the base formation molders 4250′and 4260′ have been fully lowered the support section 16101 and thepunted section 1510′ of the base 1500′ are formed.

The blow pin 4700 can continue to blow air to cool and harden the moltenpolymer. Once the molten plastic has been sufficiently cooled andhardened, the press raises the base formation molders 4250′ and 4260′along the y-axis 4204 away from the transition points 4270′ and 4280′,as indicated by arrows 4620, opens the mold 4200′ by moving the opposingmolders of the mold 4200′ away from each other, as indicated by arrows4520, and lowers the blow pin 4700, as indicated by 4720, to release thenewly formed filter tank.

Referring to FIGS. 1 and 26-44, an exemplary embodiment of theunderdrain 2000 can be formed using two selectively interlockingcomponents 2100 and 2500. The underdrain 2000 can be inserted into afilter tank at or near the bottom of the filter tank and can operate topermit water from within the filter tank to enter the underdrain, butprevent filtrate material, such as sand, from entering the underdrain2000. In the present embodiment, the component 2100 can form a bottom ofthe underdrain 2000 and the component 2500 can form a top of theunderdrain 2000. The components 2100 and 2500 can be selectively coupledby inter-component locking structures 2800. The component 2100 caninclude a first locking member 2810 of the inter-component lockingstructure 2800 and the component 2500 can include a second lockingmember 2820 of the inter-component locking structure 2800. The first andsecond locking members 2810 and 2820 can be configured to interlock thecomponent 2100 to the component 2500 to form the underdrain 2000.

In exemplary embodiments, the components 2100 and 2500 can bepreassembled to form the underdrain 2000 before being disposed within afilter tank such that the assembled underdrain 2000 can have dimensionfigured to pass through an opening in the filter tank. For example, theunderdrain 2000 can have a width, height, and/or length that is narrowerthan a width or diameter of an opening (e.g., first port 1110) in thefilter tank (e.g., filter tank 1000). In the present example, theunderdrain 2000 can pass through the opening without adjusting,manipulating, reconfiguring, or the like, a structure of the assembledunderdrain 2000.

In exemplary embodiments, at least one dimension of the underdrain 2000is greater than a width or diameter of the opening in the filter tankthrough which the underdrain 2000 passes to dispose the underdrainwithin the filter tank. For example a length of the assembled underdrain2000 can be greater than the diameter of the opening in the filter tankthrough which the underdrain 2000 passes to dispose the underdrainwithin the filter tank such that once the assembled underdrain 2000 isoriented for operation within the filter tank, the dimensions of theunderdrain prevent removal of the underdrain from the filter tank. Theconfiguration and dimensions of the underdrain 2000, for example havingat least one dimension that is greater than the opening through whichthe underdrain 2000 passes to be disposed within the filter tank, canfacilitate uniform operation of a sand filter unit to reduce and/orprevent channeling in the sand and/or to facilitate uniform distributionof water during a backwash operation.

Referring to FIGS. 26-35, the bottom component 2100 can have an outersurface 2110, an inner surface 2150, the first locking members 2810,bracing members 2160, and drainage openings 2200, such as slits, slots,apertures, holes, channels, and the like. As shown in FIG. 27, forexample, the outer surface 2110 can include a generally flat or planarsection 2112 and generally curved side section 2114 extending to atiered edge 2116 forming an inner and outer perimeter of the bottomcomponent 2100 and defining an interior area 2118 of the bottomcomponent 2100. Filter tank mounting members 2120 can be disposed on theplanar section 2112 of the outer surface 2110 to facilitate mounting ofthe underdrain 2000 on a bottom inside of a filter tank, which can havecorresponding underdrain mounting members, such as underdrain mountingmembers 1540. The filter tank mounting members 2120 can include raisedportions 2122 extending away from the planar section 2112. The raisedportions 2122 can be curved along the outer surface 2110 and can beconfigured to interface with the corresponding underdrain mountingmembers 1540 of the filter tank 1000. The raised portions 2122 can havean opposing relation such that concave portions of the raised portions2122 face each other.

Referring to FIGS. 30 and 32-34, for example, the tiered edge 2116 caninclude a first section 2124 that is generally parallel to the planarsection 2112 of the outer surface 2110, a second section 2126 that isgenerally perpendicular to and extends from and inner end 2128 of thefirst section 2124 and, and a third section 2132 extending generallyperpendicularly from the second section 2126 and generally parallel tothe first section 2124. The first section 2124 of the tiered edge 2116can have a width 2134 forming a lip about an outer perimeter of thetiered edge 2116 upon which a portion of an edge of the top component2500 can rest when the components 2100 and 2500 are interlocked. Thesecond and third sections 2126 and 2132 of the tiered edge 2116 canextend into an interior area of the component 2500 when the components2100 and 2500 are interlocked. The second section 2126 can form a guidefor receiving and aligning the components 2100 and 2500 to facilitateinterlocking of the components 2100 and 2500, and can provide a barrierwith the edge of the top component to prevent filtrate material fromentering the underdrain between the edges of the components 2100 and2500. The third section 2132 can have a width 2138 forming a lip aboutan inner perimeter of the tiered edge 2116.

As shown in FIGS. 29-33, for example, the inner surface 2150 of thecomponent 2100 generally conforms to the outer surface 2110 such thatthe planar section 2112 and curved side section 2114 are reflectedgenerally as a planar section 2152 and a curved side section 2154 on theinner surface 2150. The bracing members 2160 can extend from the innersurface 2150 into the interior area 2118 of the component 2100, and insome embodiments, can extend to be substantially flush with the thirdsection 2132 of the tiered edge 2116 so that a tip 2162 of the bracingmembers 2130 extends into the top component 2500 when the components2100 and 2500 are interlocked. The bracing members 2160 can have agenerally elongate cylindrical or rod-like body and can extend generallyperpendicularly from the planar section of the inner surface 2150. Thebracing members 2160 can include a recess 2164 at the tip 2162 thatcorresponds to a length 2166 of the second section 2126 of the tierededge 2116 such that a bottom of the recess 2164 is substantially flushwith the first section 2124 of the tiered edge 2116. The tip 2162 of thebracing members 2160 can be configured to receive a tip of the bracingmembers of the top component 2500 such that a distal end of the tip ofthe bracing members of the component 2500 abut the bottom of therecesses in the tips 2162 of the bracing members 2160.

Still referring to FIG. 26-, and more particularly to FIGS. 27, 30, and34, for example, the first locking members 2810 can be distributedabout, inward of, and proximate to a perimeter of the tiered edge 2116.The first locking members 2810 can be projections, each having agenerally rectangular body section 2812 with a length 2817 and a width2818, and a retaining section 2814 extending from a distal end 2819 ofthe rectangular body 2812. The rectangular body sections 2812 of thefirst locking members 2810 can be substantially perpendicular to thesecond section 2126 of the tiered edge 2116, and therefore,substantially perpendicular to the planar sections 2112 and 2152. Therectangular body section 2812 can extend outward from the interior area2118 to extend beyond the tiered edge 2116. The retaining section 2814of the first locking members 2810 can protrude from the body section2812 to provide a lip 2816. The first locking members 2810 can beresilient members that can be urged and/or deflected inwardly withrespect to the perimeter of the tiered edge 2116 and subsequently canreturn or spring back to their nominal position.

The drainage openings 2200 can be formed during the molding of thebottom component and can be dimensioned to permit water to pass through,but to prevent filtrate material from passing through. The drainageopenings 2200 can be distributed about the outer surface 2110 of thebottom component 2100 and extend through a wall of the bottom component2100 defined by the outer and inner surfaces 2110 and 2150 to facilitatecommunication between an interior and the exterior of the underdrain2000. As shown in FIG. 35, the drainage openings 2200 can be taperedsuch that the drainage openings 2200 can start with a narrow outeropening 2210 in the outer surface 2110 of the bottom component 2100 cangradually widen towards an inner surface 2150 of the bottom component2100. The drainage openings 2200 can be wider at the inner surface 2150than at the outer surface 2110 to encourage water to more freely flowinto the underdrain 2000 after passing through the outer surface 2110.The dimensions of the drainage openings 2200 at the outer surface 2110can permit water to there through, but to prevent filtrate material frompassing there through, while the dimensions of the drainage openings2200 at the inner surface can be sized without regard to the dimensionsof the filtrate material.

Referring to FIGS. 1, 26, and 36-44, the top component 2500 of theunderdrain can have an outer surface 2510, the first port 2535, and thesecond port 2540, an inner surface 2550, bracing members 2560, drainageopenings 2700, and the second locking members 2820. The outer surface2510 can include a generally flat or planar section 2512 and generallycurved side section 2514 extending to a tiered edge 2516 forming a innerand outer perimeter of the top component 2500 and defining an interiorarea 2518 of the component 2500. The first port 2535 can be disposed onthe planar section 2512 of the outer surface 2510 and can form anopening in the component 2500 to facilitate communication between aninterior and exterior of the underdrain 2000. The first port 2535 canhave a cylindrical configuration and can be configured to receive aconduit (e.g., a pipe or tube), such as the recirculation pipe 3300 fortransporting water from the underdrain 2000 to a body of water, such asa pool, and/or to permit a backwash operation. In some embodiments, thefirst port 2535 can be centered with respect the sides of the component2500. The second port 2540 can be disposed on the planar section 2512 ofthe outer surface 2510 and can form an opening in the top component 2500to facilitate communication between an interior and exterior of theunderdrain 2000. In an exemplary embodiment, the second port 2540 canhave a cylindrical configuration and can be configured as a venting portto receive a venting conduit (e.g., a pipe or tube) for venting of theinterior area of the underdrain 2000 to the atmosphere. For embodimentsin which venting is not employed, a pin 2545 (FIG. 26) can be insertedinto the port 2540 to close the port and prevent filtrate material(e.g., sand) from entering the interior area of the underdrain 2000 viathe second port 2540. For example, while FIG. 1 includes a ventingconduit extending from the port 2540, those skilled in the art willrecognize that venting can be accomplished through the port 2535 in theillustrated configuration. Furthermore, for embodiments in which theinlet and outlet ports are on the side of the housing of the filtertank, venting can be accomplished using the port 2540 and the ventingconduit In some embodiments, the second port 2540 can be proximate tothe first port 2535 and can have a diameter that is smaller than adiameter of the first port 2535. In some embodiments, the second port2540 can be offset from a center point with respect the sides of thecomponent 2500.

Referring to FIGS. 41 and 42, for example, the tiered edge 2516 caninclude a first section 2520 that is generally parallel to the planarsection 2512 of the outer surface 2510, a second section 2524 that isgenerally perpendicular to and extends from an inner end of the firstsection 2520, and a third section 2528 extending generallyperpendicularly from the second section 2524 and generally parallel tothe first section 2520. The first section 2520 of the tiered edge 2516can have a width 2522 forming a lip about an outer perimeter of thetiered edge 2516 upon which the first section 2124 of the edge 2116 ofthe bottom component 2100 can abut when the components 2100 and 2500 areinterlocked. The width 2522 of the first section 2520 of the tiered edge2516 can be substantial equal to the width 2134 of the first section2124 of the tiered edge 2116. The second section 2524 of the tiered edge2516 can interlocking interface (e.g., friction fit) with and/or abutthe second section 2126 of the tiered edge 2116 when the components 2100and 2500 are interlocked. A length 2526 of the second section 2524 ofthe tiered edge 2516 can be substantially equal to the length 2166 ofthe second section 2124 of the tiered edge 2116. Likewise, the thirdsection 2528 of the tiered edge 2516 can have a width 2530 forming a lipabout an inner perimeter of the tiered edge 2516 upon which the thirdsection 2132 of the edge 2116 of the bottom component 2100 can abut whenthe components 2100 and 2500 are interlocked. The widths of the thirdsections 2132 and 2528 can be substantially equal.

As shown in FIGS. 38, 41, and 42, for example, the inner surface 2550 ofthe top component 2500 generally conforms to the outer surface such thatthe planar section 2512 and curved side section 2514 are reflected as aplanar section 2552 and a curved side section 2554 on the inner surface2550. The bracing members 2560 can extend from the inner surface 2550into the interior area 2518 of the top component 2500, and in someembodiments, can extend to be substantially flush with the first section2520 of the tiered edge 2516. The bracing members 2560 can have agenerally elongate cylindrical or rod-like body and can extend generallyperpendicularly from the inner surface. The bracing members 2560 beconfigured to be inserted into the recess 2164 of the tip 2162 such thata distal end 2562 of a tip 2564 of the bracing members 2560 of thecomponent 2500 abut the bottom of the recess 2164 in the tip 2162 of thebracing members 2160. When the components 2100 and 2500 are interlocked,the bracing members 2160 and 2560 can form columns extending between theplaner sections 2152 and 2552 of the inner surfaces 2150 and 2550, andplaner sections 2112 and 2512 and/or planar sections 2152 and 2552 canbe generally parallel. The bracing members 2160 and 2560 providestructural support to the underdrain 2000 to reinforce the underdrain2000. The columns formed by the bracing members when the components 2100and 2500 are interlocked can be configured to support a load of thefiltrate material, such as sand, and water and pressure in the filtertank to prevent the underdrain 2000 from collapsing. In exemplaryembodiments, the bracing members 2160 and 2560 can be implemented assecond inter-component locking structures of the underdrain 2000. Forexample, the tip 2564 can be configured and dimensioned to fit tightlywithin the recess 2164 of the tip 2162 such that the tip 2564 forms afriction or interference fit within the recess 2164 and/or deforms ordisplaces the tip 2162 so that the recess 2164 conforms to theconfiguration and dimension of the tip 2564.

Still referring to FIGS. 26, 36-44, and more particularly to FIGS. 37,43, and 44, for example, the top component 2500 can include the secondlocking member 2820 to selectively interlock the top section 2500 to thebottom component 2100. The second locking members 2820 can be formed bychannels 2822 and openings 2824. The channels 2822 can be formed on theinner surface 2550 of the top component 2500 and can extend from theedge 2516 towards the planar section 2512 of the top component 2500. Theopenings 2824 can be disposed at a distal end 2826 of the channels 2822and can be configured to receive the retaining section 2814 of the firstlocking members 2810. For example, the openings 2824 can have a width2828 that is slightly wider than the width 2818 of the first lockingmembers 2810 so that the retaining sections 2814 fits within theopenings 2824. To interlock the bottom and top components 2100 and 2500,the retaining section 2814 of the first locking members 2800 slide alongthe channel 2822 of the second locking member 2820 causing the firstlocking member 2800 to deflect inwardly towards an interior of theunderdrain 2000. Once the retaining section 2814 of the first memberreaches the opening 2824 of the second locking member 2820, the firstlocking member 2800 returns and/or springs back outwardly towards itsnominal position so that the lip 2816 of the retaining section extendsinto the opening 2824 of the second locking members 2820 and catches onan edge of the opening to interlock the components 2100 and 2500 to formthe underdrain 2000.

The drainage openings 2700 can be formed during the molding of the topcomponent and can be dimensioned to permit water to pass through thedrainage openings 2700, but to prevent filtrate material from passingthrough the drainage openings 2700. The drainage openings 2700 can bedistributed about the outer surface 2510 of the top component 2500. Asshown in FIG. 40, for example, the drainage openings 2700 extend througha wall of the top component 2500 defined by the outer and inner surfaces2510 and 2550 to facilitate communication between an interior andexterior of the underdrain 2000. The drainage openings 2700 can startwith a narrow outer opening 2610 in the outer surface 2510 of the topcomponent 2500 can gradually widen towards an inner surface 2550 of thetop component 2500 such that the drainage openings 2700 are wider at theinner surface 2550 than at the outer surface 2510 to encourage water tomore freely flow into the underdrain 2000 after passing through theouter surface 2510. In some embodiments, the dimensions of the drainageopenings 2700 at the outer surface 2510 can permit water to therethrough, but to prevent filter material from passing there through,while the dimensions of the drainage openings 2700 at the inner surface2550 can be sized without regard to the dimensions of the filtratematerial.

In another exemplary embodiment of the underdrain 2000, as shown inFIGS. 45-60, the underdrain 2000 can include first and secondinter-component locking structures 2800 a and 2800 b to selectivelyinterlock components 2100′ and 2500′. The component 2500′ can includefirst perimeter locking members 2810 a of the first inter-componentlocking structure 2800 a, and the component 2100′ can include secondperimeter locking members 2820 a of the first inter-component lockingstructure 2800 a. The component 2100′ can include first interior lockingmembers 2810 b, and the component 2500′ can include second interiorlocking members 2820 b of the second inter-component locking structures2800 b.

Referring to FIGS. 46 and 53-59, the first perimeter locking members2810 a of the first inter-component locking structures 2800 a can bedistributed about and inward of and proximate to an inner perimeter ofthe component 2500′, and can be formed to include shoulder portions 2812a and solid body projections 2814 a, such as pins, extending from theshoulder portions 2812 a. The first perimeter locking members 2810 a canextend generally perpendicularly to the planar interior surface of thecomponent 2500′. In exemplary embodiments, the projections 2814 a of thefirst perimeter locking members 2810 a can be formed as cylindrical,rod-like structures that have a length 2817 a and a diameter 2818 a. Thefirst perimeter locking members 2810 a can have a rounded distal end2819 a to aid in alignment of the first perimeter locking members 2810 awith corresponding ones of the second perimeter locking members 2820 a.

Referring to FIGS. 46-52, for example, the second perimeter lockingmembers 2820 a of the first inter-component locking structures 2800 acan be formed as projections 2822 a having a shoulder portion 2813 a andrecesses 2824 a disposed inward of and proximate to an inner perimeterof the component 2100′. The shoulder portion 2813 a can provide asurface substantially surrounding the opening of the recess 2824 a andcan provide an area for interfacing with the shoulder 2812 a of thefirst perimeter locking member 2810 a. The recesses 2824 a can have adepth that corresponds to the length 2817 a of the first perimeterlocking members 2810 a. The recesses 2822 a can have a multi-sidedconfiguration such that the shape associated with the recess 2822 a isdifferent than the shape associated with the first perimeter lockingmembers 2810 a. In exemplary embodiments, the recess 2822 a can beconfigured to be square, pentagonal, hexagonal, heptagonal, octagonal,decagonal, or the like. For example, in the present embodiment, therecesses 2822 a can have a hexagonal shape. The recesses 2822 a can havea width 2828 a that is substantially equal to or less than the diameter2818 a of the first perimeter locking members 2810 a such that the firstperimeter locking members 2810 a fit securely within the secondperimeter locking structures 2820 b.

In exemplary embodiments, as the first perimeter locking structures 2810a are inserted into the second perimeter locking members 2820 a, theshape of the recess 2822 a can be deformed to accommodate the firstlocking member 2810 a to form a friction and/or interference fit betweenthe first and second locking members. For example, the sides of therecess 2822 a of the second perimeter locking members 2820 a can bepushed outwardly as the first perimeter locking members 2810 a areinserted into the recess 2822 a to accept the first perimeter lockingmembers 2810 a. In exemplary embodiments, once the projections 2814 ahave been fully inserted into the recesses 2824 a of the shoulderportions 2812 a can abut the shoulder portions 2813 a of the projections2822 a so that the first and second perimeter locking members interlockand form a structural support member to reinforce the underdrain.

Still referring to FIGS. 46-52, the first interior locking members 2810b of the second inter-component locking structures 2800 b can bedistributed inward of and spaced away from the inner perimeter of thecomponent 2100′, and can be formed as projections 2814 b having a hollowbody portion towards a distal end 2819 b of the projections 2814 b, suchas hollow pins. The first interior locking members 2810 b can extendgenerally perpendicularly from the planar interior surface of thecomponent 2100′. In exemplary embodiments, the hollow body projections2814 b can be formed as cylindrical, rod-like structures that have alength 2817 b and an outer diameter 2818 b. The first interior lockingmembers 2810 b can have a hallowed cavity that is open at a distal end2819 b of the first interior locking members 2810 b.

Referring to FIGS. 46 and 54-56 and 59, for example, the second interiorlocking members 2820 b of the second inter-component locking structures2800 b can be formed as projections 2822 b protruding and/or extendingfrom the planar interior surface of the component 2500′ such that thesecond interior locking members are disposed inward of and spaced awayfrom the inner perimeter of the component 2500′. The projections 2822 aof the second interior locking members 2820 b can include recesses 2824b in the projections forming receiving areas of the second interiorlocking members 2820 b. The recesses 2824 b can have a depth toaccommodate at least a portion of the length 2817 b of the firstinterior locking members 2820 b. The recesses 2824 b can have amulti-sided configuration, as shown in FIG. 57, for example, such thatthe shape associated with the recess 2824 b is different than the shapeassociated with the first interior locking members 2810 b. In exemplaryembodiments, the recesses 2824 b can be configured to be square,pentagonal, hexagonal, heptagonal, octagonal, decagonal, or the like.For example, in the present embodiment, the recesses 2824 b can have aoctagonal shaped. The recesses 2824 b can have a width 2828 b that issubstantially equal to or slightly less than the diameter 2818 b of thefirst interior locking members 2810 b such that the first interiorlocking members 2810 b fit securely within the second interior lockingstructures 2820 b.

In exemplary embodiments, as the first interior locking structures 2810b are inserted into the second interior locking members 2820 b, thehollow body projections 2812 b can be compressed inwardly to deform thehollow cavities of the hollow body projections 2812 b of the firstinterior locking members 2810 b so that the first interior lockingmembers fit securely in the second interior locking members to form afriction and/or interference fit between the first and second lockingmembers 2810 b and 2820 b, respectively. In exemplary embodiments, oncethe projections 2814 b have been fully inserted into the recesses 2824b, the first and second interior locking members interlock and form astructural support member to reinforce the underdrain.

Still referring to FIGS. 45-60, and more particularly to FIGS. 48-50 and54-56, for example, exemplary embodiments can include bracing members2160 a and 2160 b extending generally perpendicularly from the innerplanar surface of the component 2100′. The bracing members 2160 a canhave an elongated X-shaped configuration and can extend from the innerplanar surface of the component 2100′ to a X-shaped receiving area 2560a on the inner planer surface of the component 2500′ when the components2100′ and 2500′ are interlocked so that a distal end of the bracingmembers 2160 a engages the receiving area 2560 a and forms a supportstructure of the underdrain to prevent the underdrain from collapsingunder the load applied to the underdrain in operation. In exemplaryembodiments, the receiving area can include a recessed portion and adistal portion of the bracing member 2160 a can fit within a recessedportion to form a friction or interference fit. In exemplaryembodiments, the bracing members 2160 a and receiving areas 2560 a canform third inter-component locking structures.

The bracing members 2160 b can have a generally cylindrical, taperedelongate body and can extend from the inner planar surface of thecomponent 2100′ to a receiving area 2560 b formed in or on the innerplaner surface of the component 2500′ when the components 2100′ and2500′ are interlocked so that a distal end of the bracing members 2160 bengages the receiving area 2560 b and forms a support structure of theunderdrain to prevent the underdrain from collapsing under the loadapplied to the underdrain in operation. In exemplary embodiments, thereceiving area 2560 b can have a recessed portion and a distal portionof the bracing member 2160 b can fit within a recessed portion of thereceiving area 2560 b to form a friction or interference fit. Inexemplary embodiments, the bracing members 2160 b and the receivingareas 2560 b can form fourth inter-component locking structures.

As shown in FIG. 45, the port 2540′ can be formed to be closed off suchthat venting is accomplished through the center port 2535′ forarrangement in which the outlet port is at the top of the filter tank.For embodiments, in which the outlet port is positioned on a side of thefilter tank the port 2540′ can be drilled or other opened to allowventing through the port 2540′.

In an exemplary operation, pool water flows into the filter unit 100from a swimming pool via a water circulation system, which can includeone or more pumps positioned upstream and/or downstream of the filterunit 100. Water flowing into the filter unit 100 can pass through theinlet port and the diffuser, and can percolate through the filtratematerial, such as sand, to an exemplary embodiment of the presentlydisclosed underdrain, which collects filtered pool water forrecirculation in the pool by the water circulation system. The filteredwater can be output from the filter unit 100 to the pool via an outletport of the filter unit 100. During the circulation of the pool water,the water can pass through other water processing components. Forexample, the water can pass through a basket or skimmer componentconfigured to remove large debris, such as leaves, from the water priorto entering the filter unit 100 and/or may pass through one of morewater heating elements to heat the water.

In an exemplary backflow operation, the flow of the water is reversed byactuation of a multi-port valve such that the water flows into thefilter unit 100 via the outlet port 3120. The water entering the filterunit 100 via the outlet port 3120 flows through the recirculation pipe3300 into the underdrain and from an interior of the underdrain to anexterior of the underdrain. The backwash operation can function to cleanthe drainage openings of the underdrain by dislodging particles stuck inthe drainage openings as well as to clean the surface of the filtrationmedia. Thus, the backwash operation can be used on occasion to improvethe filtration and efficiency of the filter unit.

Experiments were performed in which both a conventional lateralunderdrain assembly, such as a conventional lateral underdrain having asimilar configuration to that of the lateral underdrain assemblydisclosed in U.S. Pat. No. 5,068,033 and an exemplary embodiment of theunderdrain of the present disclosure were tested. Experiments wereperformed using a flat bottom tank with two returns, a skimmer, a 8″Hayward suction outlet connected to the filter with piping, and aHayward TriStar pump with a Hayward Variable Speed Controller. Theunderdrains were set up on a spacer consisting of a piece of cartridgecore to enable flow through the bottom of the underdrain.

In a first experiment, pressure drop of the conventional lateralunderdrain assembly and the exemplary embodiment of the underdrain ofthe present disclosure was compared. As shown in FIG. 61, the pressureloss and a corresponding flow loss between an embodiment of underdrainand the conventional lateral underdrain assembly was comparable. Afterbackwashing, both the underdrains returned to the initial readings offlow and head loss.

In a second experiment, a dirt loading was conducted, in which dirt isadded to the filter to simulate excess dirt loading. As shown in FIG.62, the second experiment indicated that both underdrains in a cleansand filter that was dirt loaded had about the same flow capacity andabout the same pressure drop. There was no apparent “channeling” in thesand after the dirt loading test and backwashing, and the sanddistribution after the backwashing appeared to be fairly uniform.

Thus, exemplary embodiments of the present disclosure perform comparablyto a conventional lateral underdrain assembly. However, exemplaryembodiments of the underdrains of the present disclosure can bemanufactured at a reduced cost and can reduce installation times whencompared to the conventional lateral underdrain assembly becauseexemplary embodiments of the underdrains include a reduced number ofindividually manufactured components that must be assembled.Furthermore, in exemplary embodiments of the present disclosure, theunderdrain 2000 can be preassembled external to a filter tank and can beseated in the filter tank as an assembled unit without having tomanipulate, adjust, reconfigure, or the like, the structure of theunderdrain 2000.

While preferred embodiments have been described herein, it is expresslynoted that these embodiments should not be construed as limiting, butrather that additions and modifications to what is expressly describedherein also are included within the scope of the invention. Moreover, itis to be understood that the features of the various embodimentsdescribed herein are not mutually exclusive and can exist in variouscombinations and permutations, even if such combinations or permutationsare not made express herein, without departing from the spirit and scopeof the invention.

What is claimed is:
 1. A unitary pool filter tank comprising: a housingportion to receive a filtrate material; and a base portion integrallyformed with the housing portion, the base portion including a puntedsection and a support section, the punted section forming a generallyconvex inner wall portion of the unitary pool filter tank with a bumpedout portion formed about a center axis of the filter tank, the supportsection integrally connecting the punted section to the housing portion,the bumped out portion forming an underdrain mounting membercorresponding to a filter tank mounting member of an underdrain.
 2. Theunitary pool filter tank of claim 1, wherein an inward bend defines aboundary between the housing portion and the base portion, the inwardbend and a first outward bend define an outer surface of the supportsection, the first outward bend and a second outward bend define anunder surface of the support section, and the second outward benddefines a boundary between the support section and the punted section.3. The unitary pool filter tank of claim 2, wherein the outer surface ofthe support section extends generally downwardly from the inward bendand the under surface extends between the first and second outwardsbends generally perpendicularly to the outer surface.
 4. The unitarypool filter tank of claim 1, wherein the bumped out portion of thepunted section has a generally cylindrical shape with a rounded circularface to seat the underdrain.
 5. The unitary pool filter tank of claim 1,wherein the base portion further comprises an integrally formed bracedisposed under the punted section.
 6. The unitary filter tank of claim5, wherein the brace forms a cross brace, a length of the braceextending across a diameter of the punted section.
 7. The unitary poolfilter tank claim of 6, wherein a lower edge of the brace extendssubstantially linearly along the length of the brace and an upper edgeof the brace generally conforms to contours of the punted section alonga length of the brace.
 8. The unitary pool filter tank of claim 1,wherein the housing has a generally oval configuration with a first portconfigured to facilitate communication between an interior and anexterior of the unitary pool filter tank.
 9. The unitary pool filtertank of claim 1, wherein the unitary pool filter tank is formed from asingle molten polymer body.
 10. A system for filtering pool water, thesystem comprising: a unitary filter tank having an integrally formedhousing and base, the base including a punted section and a supportstructure, the punted section forming a generally convex inner wallportion of the unitary pool filter tank with a bumped out portion formedabout a center axis of the filter tank, the support section integrallyconnecting the punted section to the housing, the bumped out portionforming an underdrain mounting member, the support section integrallyconnecting the punted section to the housing; and an underdrain having afilter tank mounting member corresponding to the underdrain mountingmember to seat the underdrain on the punted section of the base, theunderdrain including interlocking first and second components, thesecond component selectively interlocking with the first component toform an interior area of the underdrain, the first and second componentshaving a plurality of drainage openings, each of the drainage openingsopening into the interior area of the underdrain and permitting fluidcommunication between an exterior and the interior area.
 11. The systemof claim 10, wherein an inward bend defines a boundary between thehousing and the base, the inward bend and a first outward bend define anouter surface of the support section, the first outward bend and asecond outward bend define an under surface of the support section, andthe second outward bend defines a boundary between the support sectionand the punted section.
 12. The system of claim 11, wherein the outersurface of the support section extends generally downwardly from theinward bend and the under surface extends between the first and secondoutwards bends generally perpendicularly to the outer surface.
 13. Thesystem of claim 10, wherein the bumped out portion of the punted sectionhas a generally cylindrical shape with a rounded circular face to seatthe underdrain.
 14. The system of claim 10, wherein the base portionfurther comprises an integrally formed brace disposed under the puntedsection, the brace having a length extending across a diameter of thepunted section, wherein a lower edge of the brace extends substantiallylinearly along the length of the brace and an upper edge of the bracegenerally conforms to contours of the punted section along a length ofthe brace.
 15. The system of claim 10, wherein the first componentinclude a first locking member distributed inward of, and proximate to,an edge of the first component, and the second component includes secondlocking member having a channel and an opening disposed at a distal endof the channel, the first locking member forming a resilient projectionhaving a body section and a retaining section, the retaining sectionprotruding from the body section to provide a lip, the channel of thesecond locking members being formed on an inner surface of the secondcomponent and extending to the opening disposed at the distal end of thechannel, the retaining section of the first locking member beingconfigured to slide along the channel causing the first locking memberto deflect inwardly towards an interior area of the underdrain, thefirst locking member returning to a nominal position when the retainingsection reaches the opening so that the lip of the retaining sectionextends into the opening and catches on an edge of the opening tointerlock the first and second components of the underdrain.
 16. Thesystem of claim 15, wherein the first component includes a first bracingmember extending from an inner surface of the first component into aninterior area of the underdrain so that a tip of the first bracingmember extends into the second component, and the second componentincludes a second bracing member extending from an inner surface of thesecond component into the interior area of the underdrain, the tip ofthe first bracing member having a recess for receiving a tip of thesecond bracing member so that the second bracing member engages thefirst bracing member to form a support column extending between theinner surface of the first component and the inner surface of the secondcomponent.